Indirect heating boiler: device, principle of operation and connection diagrams. How to choose an expansion tank for an indirect heating boiler Connection to pipes made of various materials

Article outline

If you live in a private house, then installing an indirect heating boiler together with a boiler will allow you to kill two birds with one stone - heat the house and provide constant access to hot water. We have selected for you best models water heaters that can be found on sale today - choose!

Briefly about the main characteristics

In ordinary storage water heaters the temperature of the liquid rises due to the operation of heating elements, while in boilers heating is carried out due to the circulation of a heated coolant in the system. It looks something like this: water is heated in a single- or double-circuit boiler and fed through pipes to a coil or other heat exchanger installed in the tank; at the same time, cold water enters the tank from the main, which is subsequently heated due to heat exchange through the walls of the coil. Instead of a coil, a tank-in-tank design can be provided. In this case, the coolant is supplied to the external tank, and the heated liquid is supplied to the internal one. The presence of temperature and liquid volume sensors inside the tank, as well as automatic relays, ensure the smooth operation of the equipment. Some models are also equipped with additional electric heaters - even with force majeure with a boiler, you can use hot water. Everything seems to be simple, but before buying it is necessary to understand the main technical characteristics of such equipment.

We omitted such a parameter as the thread diameter for connecting to pipes, because. this issue, if necessary, is solved by installing adapters.

Calculation of the volume of water

Only you can determine exactly the required volume, because. calculations are tied to the conditions of water consumption. Our task is to provide information that will somehow help in the choice or suggest thoughts when making the calculation. For example, we open SNiP 2.04.01-85 and see that the norms set 7.9-10.9 liters of hot water (HW) per hour per person. Following some simple calculations, we get the following table.

These calculations can only be taken into account if the water heated by the boiler is consistently used and one draw-off point is operating at the same time (only one tap is open). In practice, the given values ​​\u200b\u200bmust be multiplied by 3-5. Why is this happening? Because the norms do not take into account the desire to bask in the shower (+20 l. HW) and take a bath (+80 l. HW), wash a mountain of dishes (+20 l. HW), etc. and so on. Take into account the peak loads on the boiler - choose the volume that is most suitable for your needs.

• 50-60 liters is enough for 1 person;
• for 2-3 people you need to choose from models of 80-120 liters;
• for a family of 3-5 people, the capacity of a boiler of 120-200 liters is enough

To make it easier for you to choose the right model of equipment, we have identified four product groups depending on the volume of the storage tank: up to 100, 200, 300 and 400 liters. All specifications taken from open sources and prices are for comparison purposes only.

Important! Please note that some water heaters are only suitable for certain models of boilers. In the description, we will focus on this, but we recommend that you clarify all the nuances before buying.

Up to 100 liters

1. Baxi Combi 80 (80 liters) - from 52,500 rubles.

A notorious Italian player specializing in heating and water heating equipment, Baxi has been holding the quality mark for decades. The Baxi Combi 80 small volume boiler model is designed to work in conjunction with the LUNA-3 Comfort series boilers of the same manufacturer. Placement is floor, the water heater can be installed directly under the boiler, saving space. One of the advantages of this system is its compact dimensions. Corrosion protection is provided by the use of stainless steel and a magnesium anode. Polyurethane foam is used as thermal insulation. TENA connection is not provided.

2. Gorenje GBK80ORRNB6 (72.6 liters) - from 24,000 rubles.

When looking for a small model that can provide hot water for one or two people, pay attention to Slovenian equipment. This is a classic compact boiler with two tubular heat exchangers, the performance of which is enough for two points of water intake at once. The device is equipped with an electronic control unit and allows you to change the DHW temperature in the range of 15-75 °C. It has outlets for connecting to the boiler on the right side, two dry heating elements are installed as an additional heater. The model is equipped with several types of protection: against corrosion (magnesium anode), against freezing (effective thermal insulation), against overheating and heating without water. The manufacturer also provides a function to control legionellosis (a lung disease whose pathogens actively multiply in hot water). One of the best combined solutions in terms of price / quality ratio.

* operating parameters in flow mode are not specified by the manufacturer. The power of the heat exchanger itself is not indicated - only for the heating element.

3. Protherm FS B100S (95 liters) - from 36200 rubles.

The Czech boiler is structurally tied to the boilers of the same manufacturer - the Bear. Compact, with a concise but informative control panel, it easily fits into the kitchen interior as built-in appliances. Enamelled stainless steel, magnesium anode and antibacterial coating - all aimed at protection against corrosion and microorganisms. The tubular heat exchanger provides a high rate of heating of the entire volume of liquid: water is heated by 50 degrees in 13 minutes. To keep warm, the product is protected by a polyurethane foam coat.

4. ACV COMFORT 100 (100 liters) - from 48,000 rubles.

The Belgian manufacturer with almost a century of history offers interesting solution based on a tank-in-tank heat exchanger - model . The boiler consists of two stainless steel containers of different volumes, one of which is inserted into the other. Particular attention should be paid to the internal container: its surface is corrugated, therefore, due to thermal expansion, a change in size takes place, followed by the removal of the formed plaque of hardness salts (scale). The equipment is installed on the floor by default, but with the help of additional fixings it is possible to mount it on the wall. The heat-insulating layer is made of polyurethane foam 30 mm thick. The set of standard functions is small, but an optional control panel can be installed. It is also worth considering the lack of the possibility of recycling and connecting the heating element.

Up to 200 liters

5. Baxi Premier plus 150 (150 liters) - from 50,600 rubles.

It is possible to ensure the full operation of two hot water points with the help of. In a series of these heaters, a tubular coil-in-coil heat exchanger is used. Due to its low weight, the device can be hung on a wall or placed on the floor. The parts of the structure that come into contact with water are made of DUPLEX stainless steel, the minimization of heat losses is achieved by the use of polyurethane foam. The model is equipped with a thermostat and can be used in conjunction with any type of boilers. Optionally, it is possible to connect a tubular electric heater. The manufacturer has provided for the connection of the recirculation circuit. According to reviews, this is one of best solutions value for money for a family of four.

6. BOSCH WSTB 160 (160 liters) - from 28,000 rubles.

If a gas boiler is installed in your house, then you should think about buying a water heater. Although there is no possibility of connecting a heating element here, there is a recirculation system. The model is adapted to the harsh conditions of use in the CIS, i.e. suitable for hard water. To protect steel from corrosion, the material is coated with a special composition of glass-ceramic. There is a recirculation line so you can always count on getting water at a constant temperature. To minimize heat losses, a fur coat of 50 mm polyurethane foam is provided, the lining is made of PVC, soft. Frontal connection, it is possible to connect a temperature sensor. The entire volume is heated to ΔT=45°C in 37 minutes.

7. Protherm FE 200 BM (184 liters) - from 41650 rubles.

Many manufacturers offer storage heaters that are only suitable for their boiler models. If you have installed a Proterm boiler, then in order to satisfy requests big family in the hot water supply, it is worth considering the installation. This is an indirect floor standing boiler made of stainless steel, enameled for corrosion protection. The installed titanium anode serves the same purpose. To prevent bacteria from multiplying on the walls of the container, they are covered with a layer of antibacterial substance. Productivity is high - with a delta of 25 degrees, you can get more than 30 liters of water per minute. Without the possibility of connecting the recirculation line and heating element.

8. Gorenje GV 200 (188.9 liters) - from 25,800 rubles.

Floor water heater of indirect type Combustion GV 200 - simplicity of the device, reliability of a design and laconic design. The product is an enameled steel tank with a tubular heat exchanger inside. Installed on the floor under the boiler. An overpressure relief valve is used as protection against overheating. The device is protected from corrosion by enamel and magnesium anode. It takes up to 24 minutes to heat the entire volume of water in the tank from 15 to 75 degrees. A 40 mm thick thermal insulation layer is responsible for maintaining the temperature of the hot water supply.

* the possibility of working in flow mode is not announced by the manufacturer

Up to 300 liters

9. ACV COMFORT 240 (240 l.) - from 65,000 rubles.

Another representative of indirect water heaters that use a tank-in-tank heat exchanger. The model is able to provide hot water to three points of water intake. The product is protected from corrosion due to the use of stainless steel and a special approach to the formation of the walls of the inner tank. Here it is corrugated, which has a positive effect on its work even with very hard water. At the same time, the equipment is characterized by the same features as for products of the same series: a minimum of functions, a thermal insulation layer of 30 mm, the inability to connect a tubular electric heater and a recirculation circuit.

10. Protherm FS B300S (295 liters) - from 63,000 rubles.

This accumulator is intended for use with Proterm Grizzly or Bizon boilers. - a capacious tank with a tubular heat exchanger. There are two flanges in the tank: for installing a heating element and servicing the boiler. Enamelled surfaces that come into contact with water, as well as the presence of a titanium anode, protect equipment from corrosion. Not to mention the presence of an antibacterial coating. A layer of polyurethane insulation is responsible for reducing heat loss. The device is characterized by high performance in flow mode, it is possible to connect a recirculation line. The possibilities of this heater will be appreciated by the owners of large private houses with more than three bathrooms.

11. Baxi Premier plus 300 (300 liters) - from 70,000 rubles.

Often the main criterion for choosing a boiler is not only its volume, but also the heating rate. In this case, it is relevant to consider models with a coil-in-coil heat exchanger. - exactly what is needed! Firstly, it is compatible with any boilers. Secondly, high-quality stainless steel, perfectly protected from corrosion, is used for its production. Thirdly, with a fairly compact size and low weight, the equipment has a universal placement and is equipped with an accurate thermostat. The model allows you to supplement the system with a recirculation circuit. Connecting a heating element for 2.7 kW is optional.

Up to 400 liters

12. Drazice OKC 400 NTRR / 1 MPa (380 liters) - from 68,000 rubles.

The Czech boiler is equipped with two tubular heat exchangers, one of which is designed to be connected to a solar collector, and the second to the boiler. This allows you to save a lot on heating water on sunny days, especially in summer. If necessary, for example, a malfunction of the boiler equipment, two auxiliary electric heating elements can be mounted. The enameled tank, as well as the presence of a magnesium anode, provide long-term protection of the tank from corrosion. 50 mm rigid polyurethane foam is used as a heat-insulating layer. There is a recirculation pipe.

Information on the rate of water heating in flow mode is not provided by the manufacturer. This is due to the presence of two independent heat exchangers with different temperature conditions.

13. Bosch SK 400-3 ZB (388 l.) - from 59,500 rubles.

There are not many indirect water heaters of the capacity we are interested in in the Bosch assortment, but among them there is a special model - Bosch SK 400-3 ZB. This is an enameled tank with a stainless steel coil. Corrosion protection is represented by a magnesium anode, which has already become a natural phenomenon in such equipment. The device is quite simple: a built-in thermometer and a flange for easy maintenance. At the same time, it is possible to connect a hot water recirculation line, as well as synchronize with the boiler if the latter has an NTC sensor connector (thermal sensor). Those. you can fine-tune the operation of water heating equipment. Separately, it must be said about thermal insulation. Here it is not polyurethane foam, but made of rigid foam, which, with equal thickness, gives a lower heat-shielding effect.

14. BAXI UBVT 400 SC (395 l.) - from 58100 rubles.

If the prevailing part of the boilers is designed to work in tandem with the boiler, then the model is an exception to the rule. It is adapted for connection to a solar collector, so its purchase will be appropriate in two cases: in places with year-round sunny weather or for seasonal use. Additionally, for heating, it is possible to install electric heaters. The container itself is made of steel coated with titanium enamel - it turned out to be a corrosion-resistant and durable coating. The latter is also facilitated by the presence of a magnesium anode. The kit includes a thermometer for temperature control, there are sockets for connecting sensors. The design provides a flange for monitoring the condition of the coil, as well as a built-in pipe for recirculation.

15. Hajdu STA 400 C (400 liters) - from 64,100 rubles.

The model from the notorious Hungarian manufacturer is interesting in that with one heat exchanger, fine-tuning of the equipment is possible. So, in the cold season, such an indirect heating boiler can be configured to work in tandem with the boiler, while in the summer it can be connected to a solar collector. In the latter case, if necessary, the heating element is additionally connected. The tank and heat exchanger are protected from corrosion by a layer of hot enamel and a magnesium anode. To minimize heat loss, the container is covered on the outside with a layer of polyurethane foam protected by a plastic casing. A branch pipe is provided for connecting a DHW recirculation system.

In the next video, this boiler is presented in section.

Editor's Choice

For ease of comparison, we will enter the main characteristics in the table and decide on the most successful models. To make it clearer, we choose a boiler for 1-2 people, 2-4 people, 4-6 people. (marked in the table below in bold from top to bottom, respectively). Because not all manufacturers adhere to uniform standards when designing technical documentation, for example, not everyone indicates the value of performance in the flow mode, then we introduce the characteristic N. It shows the ratio of the unit of power per 1 liter. water. Those. we simply took and divided the capacities indicated by the manufacturer by the useful volume of drives. The larger this value, the faster the heating takes place.

Accumulative water heaters powered by electricity provide the required flow of hot water, but they take a long time to gain temperature - 1.5 ... 2 hours, depending on the volume of the tank. A more attractive option is a special container for hot water, heated by a heating boiler for 10-30 minutes, the difference is noticeable. The purpose of the publication is to explain to users what an indirect heating boiler is, to consider the design of the unit, to give practical advice by choosing and connecting the drive with your own hands.

2 types of DHW storage heaters

A household indirect heating boiler is a metal tank with a volume of 50 ... 300 liters, which uses an external heat source for preparing hot water - a boiler or a solar collector, less often a geothermal installation (). According to the device and principle of operation, water heaters are divided into 2 types:

1. The most common option is with a heat exchanger in the form of a coil made of copper or stainless steel.
2. Tank-in-tank design, where the heating element is an internal stainless steel container.

The storage tank is given a cylindrical or other shape, but always with rounded ends. Since the water pressure often reaches 6-8 bar, a welded rectangular tank (from the English tank) will not last long - the flat walls will bend from the pressure of the water, the container will burst at the seams.

Reference. Some models of double-circuit gas boilers are equipped with indirect heating tanks located inside the heat generator, as shown in the photo below. Built-in storage capacity does not exceed 80 liters.

To clarify the situation as much as possible and help you choose a water heater, we will give detailed description each type of indirect boilers.

Appliances with spiral heat exchanger

A capacitive boiler of this type consists of the following elements:

• indirect heating tank, made of stainless steel or ferrous metal, covered with heat-resistant enamel;
• the metal tank is equipped with branch pipes for connection to water supply network and immersion sleeves for mounting thermostats or temperature sensors;
• installed inside the tank a heating element- a spiral coil connected to the heating system of a private house;
• to protect the steel vessel from the effects of electrochemical corrosion, a magnesium or titanium anode is used, which is gradually destroyed during operation;
• outside the tank is insulated with polyurethane foam 30-50 mm thick, the front skin is painted thin sheet metal or a casing made of polypropylene;
• the dial thermometer scale is displayed on the front part of the device.

Note. Sometimes manufacturers supply their products with a nozzle with an emptying valve, an automatic air vent and other useful additions.

The principle of operation of the boiler is quite simple: a coolant with a temperature of 70-90 ° C is fed into the coil through the upper pipe, quickly heating the entire volume of water in the tank. The cooled coolant is returned to the boiler through the lower branch pipe.

Hot water is taken from the upper zone of the tank, replenishment is provided from below. Loading (heating) to the set temperature is controlled by a thermostat and a three-way valve included in the boiler piping circuit, which we will analyze later.

Information for comparison. The indirect water heat exchanger develops power from 12 kW (tank 80 l) to 25 kW (200 l) when heated by 45 degrees, the temperature of the boiler water is 80 ... 90 ° C. In used heating elements with a capacity of 1.5 ... 2.5 kW. The maximum heating time for 100 liters of water is 43 and 240 minutes, respectively, the minimum is 25 and 150 minutes (according to the French manufacturer Atlantic).

We examined a relatively cheap model of a single-circuit water heater. What other types of devices can be found on sale:

An important point. In wall-mounted versions of boilers, the fittings are located at the bottom, and inside the tank there is a hot water intake pipe from the upper layers. In floor models, the connecting threads are located on the top or side of the apparatus, and the tube is lowered to the bottom of the tank from the cold water supply fitting. How the water heater works, look at the video:

Tank-in-tank design

Outwardly, the boiler does not differ from its "brother" - a cylindrical insulated body, pipes for connecting heat-carrying and sanitary water, a thermometer scale. From the inside, the water heater is arranged differently:

1. The outer tank, made of ordinary carbon steel, serves as a water jacket for the inner tank. A coolant heated to 80-90 °C circulates between the walls of two vessels.
2. The inner cylindrical container is welded from stainless steel.
3. Inside the heated container, the temperature sensor sleeve and the water supply / withdrawal pipe are lowered (depending on the orientation of the housing in space). There is no magnesium anode.
4. The useful capacity of the DHW circuit is approximately 70% of the total volume of the boiler.
5. The heat output of a 100-liter unit reaches 18 kW with a heating surface of 1.03 m², a full load time of 10 minutes (according to the Belgian manufacturer ACV).
6. The heated boiler is able to function in flow mode - the heat exchange area is enough to produce hot water "on the go". One condition: boiler equipment must provide the required coolant flow. For example, a 100 l model (DHW tank - 70 liters) can request 1.5 ... 2.5 tons of coolant per hour.

In the above diagram, which shows the tank in section, the wavy profile of the tank walls is clearly visible, made for the following reasons:

• the corrugated structure of the side walls allows the vessel to increase / shrink when the water is heated / cooled;
• the area of ​​heat exchange increases;
• the mobility of the wavy profile provokes self-cleaning of internal surfaces from scale.

Water heaters "tank inside the tank" are also offered in a combined version - with a direct heating element. The tubular element automatically turns on when the contents of the boiler cool down to certain temperature or works in the summer when the heating equipment is turned off. The temperature is set by the user using an electronic control unit.

Clarification. Unlike electric boilers, the heating element heats the boiler coolant, and not sanitary water inside the stainless tank.

Double-wall indirect heating water heaters are more efficient and durable, manufacturers declare guarantee period service 5-10 years. An additional plus is simplified maintenance, the user does not need to check the condition of the magnesium anode and bother with replacement every 2 years. Now for the cons:

• a heating jacket takes up 25-30% of the useful volume of the tank, a traditional coil - up to 10%;
• models equipped with an electric heating element cannot be mounted horizontally;
• The unit is only transported in an upright position.

Note. Boilers designed for horizontal installation are attached to the wall with a "cold" pipe from top to bottom.

A significant drawback of water heaters is a decent cost. Let's compare 2 units that are comparable in quality: ACV SMART LINE E 300 and DRAZICE OKC 300 NTRR with a total volume of 300 liters. Belgian heater ACV "tank inside the tank" will cost 1720 USD. e., the price of the Drazice boiler with a coil is 750 c.u. e. The Czech model with two heat exchangers is half the price of a single-circuit "Belgian".

Choosing an indirect boiler

To choose the right indirect heating tank for a private house or apartment, find out the following points:

1. The number of permanent residents and the mode of water withdrawal. The goal is to calculate the total consumption of domestic hot water.
2. The capacity of the water heater is limited by the capacity of the boiler and solar collector. If the heat source has not yet been installed, select heating equipment taking into account the power reserve of 50-100% for loading the boiler.
3. Allocate a place for placing the device and consider the method of installation - wall or floor.
4. Decide on the functionality of the heater - do you need a heating element, a second heat exchanger.

Advice. When choosing the location of the storage tank, consider the nuance: an expansion tank is placed next to the boiler, whose volume is 10% of the capacity of the main tank. The best option accommodation in a country cottage - boiler room.

We propose to calculate the consumption of water from the DHW system according to the minimum indicators. 1 person needs 20 liters per day warm water for washing (shower) and 12 liters - for household needs, in total - 32 liters. So a family of 2 you will need a boiler with a useful volume of 50 ... 80 liters, for three residents - at least 100 liters. If you want to fill the bath, choose a tank of 120 liters or more. A simplified selection algorithm is shown in the table:

The heating rate of the tank is highly dependent on the power of the heat generator. If the building is heated by a 10-15 kW boiler, it is pointless to install a 200-liter drive - while the water heats up, the house will have time to cool down. The fact is that the priority of loading the boiler is higher than heating. Simplified: until the barrel warms up to the desired temperature, the radiator network will not receive the required amount of heat.

Here is an example of calculating the power of the boiler:

1. Initial data: the volume of the boiler is 200 liters, the temperature in the cold water system is plus 10 ° C, the hot water supply is 50 degrees.
2. To heat 1 kg of water by 1 degree, 1.16 W of thermal energy is required. We consider the heat consumption for 1 hour: 1.16 x 200 x (50 - 10) = 9.28 kW.
3. To cut the loading time by a factor of four (to 15 minutes), you need to apply 4 times more energy - 9.28 x 4 = 37.12 kW. Result: the power of the heating unit in the maximum mode is 40 kW, otherwise the boiler will take longer to heat up.

Note. The thickness of the metal walls of the working tank can be estimated by the weight of the tank. A high-quality 80 l boiler made of 2 mm metal will “tighten” about 25 kg.

Iron tanks, covered with heat-resistant plastic enamel with the addition of zirconium, are almost as reliable as stainless ones, but they are much cheaper. The weak point of stainless steel is welds, which successfully corrode in the event of a complete depletion of the magnesium anode. By the way, it is better to choose a product with a titanium electrode - it lasts three times longer.

Tying the "indirect" with the boiler

First of all, the unit must be installed on the floor or securely attached to a main wall made of brick or concrete. If the partition is built of porous materials (foam block, aerated concrete), from wall mounting better to refrain. When installing on the floor, keep a distance of 50 cm from the nearest structure - a clearance is required for servicing the boiler.

Important. Before mounting the wall-mounted horizontal boiler model, carefully read the instructions. Usually the device is hung in such a way that the cold water pipe is at the bottom. If the tank is turned upside down, the coil and the heating element will be in the upper zone, which is unacceptable.

Connecting the boiler to a solid fuel or gas boiler that is not equipped with an electronic control unit is carried out according to the diagram below.

Comment. For normal operation of the loading circuit, a pump 25-40 is enough (pressure - 0.4 bar). The element can be installed on the return or supply line - there is not much difference. The installation manual for DRAZICE water heaters shows a piping diagram where the pumping unit is in the supply.

Similarly, the heater is connected to more complex systems with several boilers and heating circuits. The only condition: the boiler must receive the hottest coolant, therefore it crashes into the main line first, and it is connected directly to the hydraulic arrow distribution manifold, without a three-way valve. An example is shown in the primary/secondary ring tying diagram.

When it is required to connect a tank-in-tank boiler, the manufacturer recommends using an expansion tank and a safety group connected to the coolant outlet. Rationale: when the internal DHW tank expands, the volume of the water jacket decreases, there is nowhere for the liquid to go. Applied equipment and fittings are shown in the figure.

The easiest way is to connect the indirect heating boiler to wall-mounted boilers, in which a special fitting is provided. The remaining heat generators, equipped with electronics, are connected to the water heater via a motorized three-way diverter valve controlled by the boiler controller. The algorithm is this:

1. When the temperature in the tank drops, the thermostat signals the boiler control unit.
2. The controller gives a command to the three-way valve, which transfers the entire coolant to the loading of the DHW tank. The circulation through the coil is provided by the built-in boiler pump.
3. Upon reaching the set temperature, the electronics receives a signal from the boiler temperature sensor and switches the three-way valve to its original position. The coolant goes back to the heating network.

An important nuance. The above scheme is also used when tying the drive with a gas boiler. It is unacceptable to dock the "indirect" with the DHW line of the heat generator.

The connection of the solar collector to the second boiler coil is shown in the following diagram. The solar system is a full-fledged closed circuit with its own expansion tank, pump and safety group. Here you can not do without a separate unit that controls the operation of the collector according to the signals of two temperature sensors.

Video: the simplest scheme for connecting a wall-mounted boiler

Water side connection

If the tapping points are located near the heating tank, the connection is made according to standard scheme below. Let's explain the functions of some elements:

• a pressure reducer is recommended for pressure surges above 6 bar;
• check valve on the supply of cold water does not allow the tank to empty into the water main;
• the expansion tank compensates for the increase in the volume of the heated liquid;
• a safety valve set to 7 bar discharges water into the sewer in the event of an increase in pressure to a critical level;
• the drain valve is used to drain water according to the method of communicating vessels.

Attention! Use in harness expansion tank, designed for water supply systems and designed for higher pressure - 6 ... 8 Bar. The heating container is not suitable - the membrane will quickly become unusable.

When consumers are away from the boiler, it is worth putting a recirculation line with an additional pump and a check valve. If your heater model does not have a separate fitting to connect this line, simply cut the return line into the cold water inlet line.

Before starting a system with a tank-in-tank type water heater, you must first fill the internal tank with sanitary water, only then pump in the coolant and carry out pressure testing. Details will tell the master on the video:

Wiring diagram

The combined version of the tank, equipped with a heating element, must be connected to the house electrical network, taking into account the transition to summer mode, in which the main coil will no longer receive heat from the boiler. We suggest using a universal circuit, which includes a pump control module by means of a thermostat.

The circuit uses a second safety thermostat, which is triggered when the sanitary water overheats. Lamp - the indicator signals the inclusion of the heating element.

Conclusion

Indirect heating devices have many advantages over and electrical installations. There are also disadvantages - the dimensions of the tanks, more complex installation and the inevitable heat losses during operation in standby mode. But the listed disadvantages recede into the background before the comfortable hot water supply, which is provided by the storage boiler, which works in tandem with the boiler.

Increasingly in heating systems alternative double-circuit boilers use boilers of indirect heating or the so-called "tank in the tank". When it is necessary to supply a large amount of water, at several points of draw-off "Tank in tank" become indispensable helpers. Stainless steel boiler suitable for country houses, office and industrial buildings.
"Tank in a tank" are becoming more and more popular in the heating market. Working with heat generated by any other energy sources is the main advantage, since water is not heated directly from electrical energy, solid fuel or gas. Boilers with indirect heating do not overload the power grid, do not need a chimney.
Working principle "Tank in a tank"
The indirectly heated stainless steel boiler is manufactured according to the tank-in-tank principle. It works on the basis of two tanks. The first container is internal, filled with heated sanitary water, the second container - the outer one contains a coolant - it is he who heats the sanitary water. Thus "tank in tank" eliminates a large number of disadvantages inherent in conventional water heaters with a coil.

The main advantages of the indirect heating boiler:
1. More hot water taps are provided due to the increased heat transfer area. Also, a short heating time for newly supplied cold water.
2. Water heaters made according to the tank-in-tank scheme have a smaller volume than was required when using a conventional water heater to ensure a given performance.
3.Sanitary requirements are met by the numerous advantages of stainless steel.
4.The use of reliable thermal insulation and self-cleaning effect of descaling results in saving energy consumption
5. Possibility of regulation of heating of sanitary water, due to the built-in thermostat.
6. Long service life

In rooms without a center of a lysed hot water supply system, tank-in-tank boilers are an indispensable assistant.
Boilers can be divided into indirect and direct heating boiler.

The advantages of indirect boilers (for example, boiler, WESTER or) use the heat converted by heating boilers and are intended for economical hot water supply of apartments, office and industrial buildings, cottages.

IN gas water heaters direct heating circuit is used. The advantage of this type of boiler is stability and sometimes independence from electricity and other factors.
The advantages of indirect boilers (for example, the acv smart boiler) are the speed of heating and the possibility of using it for several points of water consumption. During a water shutdown, the indirect agent ensures its continuous supply. The volume of the tank can reach 1000 liters. Enormous energy savings!

You can buy indirect heating boilers in the section.

The need for an expansion tank for domestic hot water is constantly being challenged. Moreover, for many experienced plumbers, the inclusion of a node in the hot water supply system causes at least bewilderment. On the other hand, many manufacturers of plumbing equipment recommend installing a tank for indirect heating boilers. The purpose of the node is quite simple: to reduce the load in the system and eliminate water hammer.

Even an approximate calculation of the expansion tank for an indirect heating boiler will show that its minimum volume will be at least 10% of the water contained in the BKN. And this is an additional capacity of 10-20 liters, occupying a usable area. Not surprisingly, one of the most common questions asked by specialists is related to how much an expansion tank is needed for hot water. To answer it, you need to understand the device and the principle of operation of the equipment.

Why do you need an expansion tank for BKN

Control the intensity of combustion and heat transfer of the boiler for solid fuel despite not all the equipment used is quite problematic. When heated, the water expands and creates excess pressure in the system, which leads to water hammer.

Membrane tank eliminates pressure drops and protects water taps, pipes and the boiler itself from damage. It happens like this:


Inside the indirect heating boiler there is a heating element connected to the heating system. When the coolant overheats, the DHW temperature rises, the load on the pipes and important structural elements, which leads to damage to expensive plumbing equipment.

The principle of operation of the expansion tank with the BKN safety group is to prevent high pressure in the DHW system and the occurrence of water hammer. There are non-return and relief valves to help in emergency situations.

Connecting the safety group and expansion tank necessary condition For long work BKN, as well as free maintenance. Equipment manufacturers often refuse warranty repairs if safety equipment is not installed in the boiler piping.

How to calculate the volume of the expansion tank for BKN

• a boiler of 100 liters is connected to a tank of at least 10 liters;
• 200 liter water heater, needs a 20 liter tank.

• Selection of an expansion tank for BKN for its intended purpose. The water in the hot water supply is more aggressive than in the heating system. The technical documentation for the buffer tank should indicate the main purpose. You can only put a tank on the boiler, the instructions of which indicate the possibility of using it for hot water supply.
• Calculation by pressure - the choice of an expansion tank for BKN is facilitated by special selection tables. Input parameters: what initial air pressure should be in the expansion tank for the DHW boiler:

  Maximum pressure Рmax, bar	Initial gas pressure Р₀, bar

• The choice of the membrane - the rubber used in the tank affects the quality of the liquid supplied to the hot water supply and the service life of the safety tank. Common materials for the manufacture of membranes:

  	Natural rubber rubber for potable and non-potable water. Operating temperature range from -10 to +50°С. Elastic, but allows partial diffusion of water. Scope - accumulation of cold water.
  	Synthetic butyl rubber for potable and non-potable water. Operating temperature range from -10 to +100°С. Less elastic than NATURAL, but durable in terms of water resistance. Scope - water supply stations (the most versatile material).
  	Synthetic ethylene/propylene rubber for potable and non-potable water. Operating temperature range from -10 to +100°С. More moisture permeable than butyl.
  	It is used only for non-potable water (heating boilers). Operating temperature range from -10 to +100°С. Less elastic.
  	Used for active media (oils, fuels). Operating temperature range from -10 to +100°С.

• Selection based on the coefficient of thermal expansion of system fluids:

To facilitate calculations, you can use special online calculators. In the initial parameters, you will need to enter the volume of the boiler. After that, the program will calculate the volume and initial pressure in the gas cavity.

The hydraulic tank for hot water supply has a blue body (white), for heating it is red.

Connection diagram for a boiler with an expansion tank

• Water is supplied to the BKN through a check valve. Such a measure will prevent the flow of heated coolant into the cold water system.
• It is better to place the expansion tank in the DHW system between the non-return valve and the boiler. This is necessary so that when the tap is opened, the user immediately receives hot water.
  It is allowed to connect the expansion tank to the BKN when the RB is placed after the boiler. There will be no functional differences in the operation of the security group. At the same time, cooled water from the Republic of Belarus will first enter the hot water supply, which is not entirely comfortable.

If the piping of the boiler with the expansion tank is done correctly when heating the DHW, the safety valve will not work. It is important to avoid two extremes:

• Expansion tank transfer- in this case, the pressure will squeeze out all the water from the tank. Consequences: water hammer and damage to plumbing equipment when water overheats. You need to reduce the pressure in the tank. To calculate the initial parameters, you can use the table above.
• Underestimated indicators of RB- when the coolant is heated, the safety valves will be torn off. Accordingly, the effectiveness of the security group will be reduced to zero. If you do not raise the pressure in the tank, even with a slight overheating of the coolant, the safety group will work.